Microbiota Transfer Therapy for Adults With Autism Spectrum Disorder (ASD) Who Have Gastrointestinal Disorders

For adults ages 18-60 years with ASD and gastrointestinal problems, the investigators propose a Phase 2 clinical trial to evaluate the safety and efficacy of MTT. The study will also determine if longer treatment is beneficial, and to conduct a longer observation after treatment stops to determine long-term safety and efficacy. The three parts of this trial are described below. Part 1: Placebo-Controlled Treatment The trial will begin with a randomized, double-blind, placebo-controlled trial which will include a 2-week treatment with oral vancomycin (or placebo), then 1 day of Moviprep to cleanse the bowel of vancomycin and bacteria/feces (all participants, since its bowel-emptying effect cannot be blinded), followed by oral administration of Full Spectrum Microbiota (FSM) or placebo. An initial high dose of FSM (or placebo) for two days will be followed by a lower maintenance dose of FSM (or placebo) for 8 weeks. Part 2 Extension and Cross-Over * For the treatment group from Part 1, there will be an 8-week extension of the maintenance dose, to determine if longer treatment has additional benefits. * For the placebo group from Part 1, they will receive MoviPrep, an initial high dose of FSM for 2 days, and then a lower dose of FSM for 8 weeks (similar to the treatment group in Part 1, but without the vancomycin). This will help us determine if pre-treatment with vancomycin is needed or not. Part 3: Follow-up There will be follow-up evaluations at 6, 12, and 18 months after treatment is stopped, to assess long-term efficacy and possible adverse effects.